Conventionally, JP-A-2008-264902 teaches a manufacturing method of a semiconductor device including an etching step for etching single crystal silicon.
In the above manufacturing method, a SOI substrate including a base layer made of single crystal silicon, an intermediate layer made of oxide silicon and an upper layer made of single crystal silicon, which are stacked in this order, is used. An oxide film patterned on the surface of the upper layer is used as a mask. Then, the upper layer is etched so as to reach the intermediate layer. Then, the intermediate layer is etched with using an etchant such as HF acid.
Accordingly, in the above manufacturing method, it is necessary to etch the intermediate layer in a lateral direction of thereof, which is parallel to the surface of the base layer, and further, to etch the upper layer in a depth direction, which is perpendicular to the surface of the base layer, so that a movable portion and a fixed portion are formed. However, since an etching rate of the intermediate layer made of oxide silicon is low, and the upper layer made of single crystal silicon is directly etched, it is difficult to improve the etching speed.